Surface sizing composition, method of production, and use thereof

ABSTRACT

The present invention relates to a surface sizing composition comprising a metal salt, wherein the metal has at least 3 valence electrons, and an aqueous polymer dispersion, wherein the aqueous polymer dispersion is an aqueous polymer dispersion (A) obtainable by free radical emulsion copolymerizing a first ethylenically unsaturated monomer blend comprising (a) 0 to 75% by weight of at least one optionally substituted styrene, (b) 15 to 100% by weight of at least one C1-C4-alkyl (meth)acrylate, and (c) 0 to 10% by weight of other ethylenically unsaturated copolymerizable monomers, wherein the sum (a)+(b)+(c) is 100%, in the presence of a water-soluble redox system comprising a first free radical initiator for the free radical emulsion copolymerization and an aqueous prepolymer composition (B) obtainable by free radical emulsion copolymerizing in a polymerization solvent comprising C1-6-carboxylic acid and C1-6-carboxylic acid anhydride, a second ethylenically unsaturated monomer blend comprising (i) 5 to 50% by weight of at least one ethylenically unsaturated quaternary amine selected from quaternary salt of N,N,N-tri(C1-4-alkyl)amino C1-4-alkyl(meth)acrylate with a mineral acid or an organic acid and/or quaternary salt of N,N,N-tri(C1-4-alkyl)amino C1-4-alkyl(meth)acrylamide with a mineral acid or an organic acid, (ii) 0 to 40%, preferably 0%, by weight of at least one ethylenically unsaturated tertiary amine selected from N,N-di(C1-4-alkyl)amino C1-4-alkyl(meth)acrylate and/or N,N-di(C1-4-alkyl)amino C1-4-alkyl(meth)acrylamide, (iii) 10 to 95% by weight of at least one optionally substituted styrene, (iv) 0 to 50% by weight of at least one C1-C4-alkyl (meth)acrylate, and (v) 0 to 10% by weight of other ethylenically unsaturated copolymerizable monomers, wherein the sum (i)+(ii)+(iii)+(iv)+(v) is 100%, in the presence of a second free radical initiator, and adding water to the obtained polymer dispersion to obtain the aqueous prepolymer composition. The present invention further relates to production thereof and use on cellulosic materials.

FIELD OF THE INVENTION

The present invention relates to surface sizing chemicals, productionmethods and uses within papermaking.

BACKGROUND

Sizing agents are widely used in the paper industry. Sizing is used tochange the characteristics of the obtained paper materials. By additionof sizing agent absorption and wear characteristics may change. Theobtained paper product may obtain a change in hydrofobation.

Sizing agents may be added during the production of the material so thatthey may either be incorporated into the paper structure as internalsizing agents or applied to the surface of the paper product beingproduced as surface sizing agent. Internal sizing chemicals arepreferably added in the wet end of the papermaking process, e.g.together with the fibers. Internal sizing chemicals are presentthroughout the paper material and thus more may need to be addedcompared to use of surface sizing agents. Surface sizing agents areprovided to improve the surface strength, printability, and waterresistance of the material to which it is applied.

Compounds that may be used as sizing agents are not always compatiblewith other additives or sizing agents. Thus, separate dosing points ofsuch incompatible components may be required. The use of separate dosingpoints may not be feasible for all paper producers due to limitations inavailable space in and around the process equipment.

There is a need for new ways to efficiently provide sizing agents to thepaper production process and new sizing agent compositions.

SUMMARY OF THE INVENTION

The present invention provides a surface sizing composition which isstorage stable. Conventional surface sizing compositions are not able toprovide a one component formula including a metal salt. Conventionalsystems may be fixed in the type of equipment used and there may not beenough space for modifications and inclusion of additional apparatuses.Paper mills which have limiting space may not be able to utilize newtechnology requiring equipment modifications. Thus, the presentinvention provides an attractive improvement for paper mills as noadditional equipment is needed as the polymeric composition and metalsalt are compatible and may be provided as a one component mixture, asthe components are not required to be kept a part in separateapparatuses and addition points. The improvements in equipment useinvolves less costs for equipment and less space in the paper machine isrequired, as additional apparatuses are not needed.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 shows sizing results of the quaternary amine polymer dispersion,and the formulate of the quaternary amine polymer dispersion withpolyaluminium chloride (PAC). PAC dose is not included in the dosecalculation of the polymeric size.

FIG. 2 shows sizing results of the quaternary amine polymer dispersion,and the formulate of the quaternary amine polymer dispersion withaluminium sulfate and alkyl ketene dimer (AKD) dispersion. AKD isincluded in the dose calculation of the polymeric size.

The lower the Cobb value the better the sizing performance.

DETAILED DESCRIPTION

The present invention relates to a surface sizing composition comprisinga metal salt, wherein the metal has at least 3 valence electrons, and anaqueous polymer dispersion.

The present invention further relates to a method of producing saidsurface sizing composition, comprising the steps of:

-   -   providing a metal salt, the metal having at least 3 valence        electrons,    -   providing an aqueous polymer dispersion,    -   mixing said metal salt and polymer dispersion to provide a        surface sizing composition to be used in papermaking.

The aqueous polymer dispersion is an aqueous polymer dispersion (A)obtainable by free radical emulsion copolymerizing a first ethylenicallyunsaturated monomer blend comprising

(a) 0 to 75% by weight of at least one optionally substituted styrene,

(b) 15 to 100% by weight of at least one C1-C4-alkyl (meth)acrylate, and

(c) 0 to 10% by weight of other ethylenically unsaturatedcopolymerizable monomers,

wherein the sum (a)+(b)+(c) is 100%,

in the presence of a first free radical initiator and

an aqueous prepolymer composition (B) obtainable by free radicalemulsion copolymerizing, in a polymerization solvent comprisingC1-C6-carboxylic acid and C1-6-carboxylic anhydride a secondethylenically unsaturated monomer blend comprising

(i) 5 to 50% by weight of at least one ethylenically unsaturatedquaternary amine selected from quaternary salt ofN,N,N-tri(C1-C4-alkyl)amino C1-C4-alkyl(meth)acrylate with a mineralacid or an organic acid and/or quaternary salt ofN,N,N-tri(C1-C4-alkyl)amino C1-C4-alkyl(meth)acrylamide with a mineralacid or an organic acid,

(ii) 0 to 40% by weight of at least one ethylenically unsaturatedtertiary amine selected from N,N-di(C1-C4-alkyl)aminoC1-C4-alkyl(meth)acrylate and/or N,N-di(C1-C4-alkyl)aminoC1-C4-alkyl(meth)acrylamide,

(iii) 10 to 95% by weight of at least one optionally substitutedstyrene,

(iv) 0 to 50% by weight of at least one C1-C4-alkyl (meth)acrylate, and

(v) 0 to 10% by weight of other ethylenically unsaturatedcopolymerizable monomers,

wherein the sum (i)+(ii)+(iii)+(iv)+(v) is 100%,

in the presence of a second free radical initiator, and adding water tothe obtained polymer composition to obtain the aqueous prepolymercomposition.

The present aqueous polymer dispersion (A) may be obtained by emulsionpolymerization of a first ethylenically unsaturated monomer blend in thepresence of an aqueous prepolymer composition (B). This stage is hereinreferred to as the second polymerization stage.

The aqueous prepolymer composition (B) may be prepared from a secondethylenically unsaturated monomer blend comprising, in particular, (i)at least one ethylenically unsaturated quaternary amine selected fromquaternary salt of N,N,N-tri(C1-C4-alkyl)amino C1-C4-alkyl(meth)acrylatewith a mineral acid or an organic acid and/or quaternary salt ofN,N,N-tri(C1-4-alkyl)amino C1-C4-alkyl(meth)acrylamide with a mineralacid or an organic acid, in the presence of a (second) polymerizationinitiator in a polymerization solvent comprising C1-C6-carboxylic acidand C1-C6-carboxylic acid anhydride. This stage is herein referred to asthe first polymerization stage.

Accordingly further provided herein is a process for the preparation ofan aqueous polymer dispersion as defined herein and hereafter,comprising free radical emulsion polymerizing, in a polymerizationsolvent comprising C1-C6-carboxylic acid and C1-C6-carboxylic acidanhydride, in the presence of a second free radical initiator, a secondethylenically unsaturated monomer blend comprising

(i) 5 to 50% by weight of at least one ethylenically unsaturatedquaternary amine selected from quaternary salt ofN,N,N-tri(C1-C4-alkyl)amino C1-C4-alkyl(meth)acrylate with a mineralacid or an organic acid and/or quaternary salt ofN,N,N-tri(C1-C4-alkyl)amino C1-C4-alkyl(meth)acrylamide with a mineralacid or an organic acid,

(ii) 0 to 40% by weight of at least one ethylenically unsaturatedtertiary amine selected from N,N-di(C1-C4-alkyl)aminoC1-C4-alkyl(meth)acrylate and/or N,N-di(C1-C4-alkyl)aminoC1-C4-alkyl(meth)acrylamide,

(iii) 10 to 95% by weight of at least one optionally substitutedstyrene,

(iv) 0 to 50% by weight of at least one C1-C4-alkyl (meth)acrylate, and

(v) 0 to 10% by weight of other ethylenically unsaturatedcopolymerizable monomers,

wherein the sum (i)+(ii)+(iii)+(iv)+(v) is 100%,

adding water to the obtained polymer composition to obtain an aqueousprepolymer composition (B) and

copolymerizing in the presence of said aqueous prepolymer composition(B) and a water-soluble redox system comprising a first free radicalinitiator for the free radical emulsion copolymerization a firstethylenically unsaturated monomer blend comprising

(a) 0 to 75% by weight of at least one optionally substituted styrene,

(b) 15 to 100% by weight of at least one C1-C4-alkyl (meth)acrylate, and

(c) 0 to 10% by weight of other ethylenically unsaturatedcopolymerizable monomers,

wherein the sum (a)+(b)+(c) is 100%

to obtain an aqueous polymer dispersion (A).

The amount of monomer(s) of group (i) is up to 50% of the total weightof the second ethylenically unsaturated monomer blend. Typically theamount of monomer(s) of group (i) is 10 to 40%, preferably 15 to 30% ofthe total weight of the second ethylenically unsaturated monomer blend.

The second ethylenically unsaturated monomer blend may also comprise upto 40% by weight of monomer(s) of group (ii) of the total weight of thesecond ethylenically unsaturated monomer blend, e.g. at least oneethylenically unsaturated tertiary amine selected fromN,N-di(C₁₋₄-alkyl)amino C₁₋₄-alkyl(meth)acrylate and/orN,N-di(C₁₋₄-alkyl)amino C₁₋₄ alkyl(meth)acrylamide. However, thepresence of unsaturated tertiary amine monomers is not required forobtaining the desired sizing properties and/or particle size. Thus thepresence of (ii) is not required in the prepolymer composition, but istolerated. Preferably the amount of monomer(s) of group (ii) is 0-15% byweight, most preferably 0%. When (ii) is present in the prepolymercomposition, the amount of (ii) should not exceed that of (i). Thus theratio of (i) and (ii) is preferably 1:<1.

The second ethylenically unsaturated monomer blend further comprises 10to 95% by weight of monomer(s) of group (iii) of the total weight of thesecond ethylenically unsaturated monomer blend. Preferably the amount ofmonomer(s) of group (iii) is 60 to 80% of the total weight of the secondethylenically unsaturated monomer blend.

The second ethylenically unsaturated monomer blend may also comprise upto 50% by weight of monomer(s) of group (iv) of the total weight of thesecond ethylenically unsaturated monomer blend. However the presencemonomers of group (iv) is not required. Thus, preferably the amount ofmonomer(s) of group (iv) is 0%.

The second ethylenically unsaturated monomer blend may also comprise upto 10% by weight of monomer(s) of group (v) of the total weight of thesecond ethylenically unsaturated monomer blend. However the presencemonomers of group (v) is not required. Thus preferably the amount ofmonomer(s) of group (v) is 0%.

In the first polymerization stage, monomers (i) to (v) are polymerizedby a solution polymerization method in a polymerization solvent whichmay also comprise water. This water is typically comprised in themonomer starting materials. Examples of C1-C6-carboxylic acids includeformic acid, acetic acid, propionic acid, and butyric acid. PreferredC1-C6-carboxylic acid is acetic acid. C1-C6-monocarboxylic acids andsaturated C1-C6-dicarboxylic acids may be used, saturatedC1-C6-monocarboxylic acids preferably being used. The saturatedC1-C6-carboxylic acids may optionally carry further substituents such ashydroxyl groups. The solution polymerization is preferably carried outin formic acid, acetic acid, propionic acid, butyric acid, isobutyricacid, valeric acid, isovaleric acid, caproic acid, hydroxypropionic acidor hydroxybutyric acid. Mixtures of different saturated C1-C6-carboxylicacids may also be used. The solution polymerization is preferablycarried out in formic acid, acetic acid, propionic acid orhydroxypropionic acid, particularly preferably in acetic acid. Examplesof C1-C6-carboxylic anhydrides include formic anhydride, aceticanhydride, propionic anhydride, and butyric anhydride. The anhydridesmay also carry substituents such as hydroxyl groups. PreferredC1-C6-carboxylic anhydride is acetic anhydride.

In the first polymerization stage, the monomers are used in relation tothe polymerization solvent in an amount such that initial prepolymercompositions having a polymer content of from 10 to 40% by weight,preferably from 13 to 20% by weight, are obtained. This does not includethe amount of water added after the polymerization stage. The aqueousprepolymer composition (B), to which water has been added, is then usedin the second stage of the polymerization. In the second stage of thepolymerization, from 0.1 to 10, preferably from 0.8 to 3, parts byweight, based on 1 part by weight of the prepolymer, of a firstethylenically unsaturated monomer blend is used.

Preferably the first polymerization stage for the preparation of theaqueous prepolymer composition (B) is performed in the presence of atleast one polymerization regulator. Suitable polymerization regulatorsinclude, for example, mercaptans, such as ethyl mercaptan, n-butylmercaptan, tert-butyl mercaptan, n-dodecyl mercaptan and tetradodecylmercaptan. When polymerization regulators are used, the amounts of thepolymerization regulator is preferably from 0.1 to 10% by weight,preferably for 0.3 to 5% by weight. The polymers prepared in the firststage have a relatively low molar mass, e.g. Mw from 1000 to 100 000,preferably from 5000 to 50 000 (as determined by size exclusionchromatography). The determination of the molecular weight distributionand of the mass average molecular weight can be carried out by methodsknown to a person skilled in the art, such as, for example, gelpermeation chromatography, light scattering or ultracentrifuging.

Monomers of group (i) include quaternary salts ofN,N,N-tri(C1-4-alkyl)amino C₁₋₄-alkylacrylates,N,N,N-tri(C₁₋₄-alkyl)amino C₁₋₄-alkylmethacrylates,N,N,N-tri(C₁₋₄-alkyl)amino C₁₋₄-alkylacrylamides,N,N,N-tri(C₁₋₄-alkyl)amino C₁₋₄-alkylmethacrylamides and mixturesthereof. The cationic groups may also originate from monomers selectedfrom 2-(dimethylamino)ethyl acrylate benzylchloride,2-(dimethylamino)ethyl acrylate dimethylsulphate, 2-dimethylaminoethylmethacrylate dimethylsulphate, and diallyldimethylammonium chloride.Preferably monomers of group (i) include quaternary salts ofN,N,N-tri(C1-4-alkyl)amino C1-4-alkylacrylates,N,N,N-tri(C1-4-alkyl)amino C1-4-alkylmethacrylates and mixture thereof.Preferred examples of group (i) include quaternary salts ofN,N,N-trimethylamino C1-4-alkylacrylates and N,N,N-trimethylaminoC1-4-alkylmethacrylates with mineral acid, such as quaternary salts ofN,N,N-trimethylamino ethyl(meth)acrylates with HCl. Particularlypreferred monomers of group (i) are[2-(methacryloyloxy)ethyl]trimethylammonium chloride and[2-(acryloyloxy)ethyl]-trimethylammoniumchloride.

Monomers of group (ii) include, for example, tertiary aminesN,N-di(C1-C4-alkyl)amino C1-C4-alkylacrylates, N,N-di(C1-C4-alkyl)aminoC1-C4-alkylmethacrylates, N,N-di(C1-C4-alkyl)aminoC1-C4-alkylacrylamides, N,N-di(C1-C4-alkyl)aminoC1-C4-alkylmethacrylamides and mixtures thereof, preferably tertiaryamines N,N-di(C1-C4-alkyl)amino C1-C4-alkylacrylates,N,N-di(C1-C4-alkyl)amino C1-C4-alkylmethacrylates and mixture thereof.Preferred examples of group (ii) include tertiary aminesN,N-dimethylamino C1-4-alkylacrylates and N,N-dimethylaminoC1-4-alkylmethacrylates, such as N,N-dimethylamino ethyl(meth)acrylates.Particularly preferred monomers of group (ii) are dimethylaminoethylmethacrylate, dimethylaminoethyl acrylate, and dimethylaminopropylmethacrylate.

The copolymerization in the first polymerization stage is effected inthe presence of a second free radical initiator. Suitable second freeradical initiators are, for example, azoinitiators such as2,2′-azobis(2-methylpropionitrile), 2,2′-azobis(2-methylbutyronitrile),or dimethyl 2,2′-azobis(2-methyl propionate) or peroxides such ashydrogen peroxide, sodium peroxo-disulfate, potassium peroxodisulfate,ammonium peroxodisulfate, dibenzoyl peroxide, dilauroyl peroxide,di-tert-butyl peroxide, tert-butyl hydroperoxide,1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, cumyl hydroperoxide orbis-cyclohexyl peroxydicarbonate. Preferably the second free radicalinitiator is 2,2′-azobis(2-methylpropionitrile), or2,2′-azobis(2-methylbutyronitrile).

The copolymerization in the first polymerization stage may further beeffected in the presences of a chain transfer agent. Suitable chaintransfer agents are, for example, sulfur compounds, e.g. mercaptans, diand polysulfides, esters and sulfides of thio- and dithiocarboxylicacids and enol sulfides. Halogen compounds, aldehydes, ketones, formicacid, enol ethers, enamines, hydroxylamine, halogenated hydrocarbons,alcohols, ethylbenzene and xylene may also be used. Examples ofregulators based on sulfur containing organic compounds includemercaptoethanol, mercaptopropanol, mercaptobutanol, thioglycolic acid,thioacetic acid, thiopropionic acid, 1-dodecanthiol, thioethanolamine,sodium dimethyidithiocarbamate, cysteine, ethyl thioglycolate,trimethylolpropane trithioglycolate, pentaerythrityl tetra(mercaptopropionate), pentaerythrityl tetrathioglycolate,trimethylolpropane tri(mercaptoacetate), butylmethylenebisthioglycolate, thioglycerol, glyceryl monothioglycolate,n-octadecyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan,butyl mercaptan, thiophenol, mercaptotrimethoxysilane andacetylcysteine. Preferably the chain transfer agent is dodecylmercaptane.

The first polymerization stage can be carried out both by a feed processand by a batch process at temperatures from 110 to 150° C., preferablyfrom 115 to 130° C. If the polymerization temperature should be abovethe boiling point of the solvent used, the polymerization is carried outunder superatmospheric pressure, for example in an autoclave equippedwith a stirrer.

The first polymerization stage is completed by addition of water toprovide the produced prepolymer as an aqueous prepolymer composition,either in a form of dispersion or solution. The concentration of theprepolymer prepared in the first polymerization stage in the aqueousprepolymer composition (B), into which water has been added is, forexample, from 10 to 40% by weight, preferably from 13 to 20% by weight.

The obtained aqueous prepolymer composition (B) is then subjected to thesecond polymerization stage where it is copolymerized with a firstethylenically unsaturated monomer blend in the presence of (first) freeradical initiators which form free radicals under the polymerizationconditions to obtain the desired aqueous polymer dispersion (A).

Examples of suitable monomers of group (a) and the group (iii) may beselected from styrene and substituted styrenes, such as α-methylstyrene,vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and mixturesthereof.

Examples of suitable monomers of group (b) and the group (iv) may beselected from C1-C4-alkyl acrylates, C1-C4-alkyl methacrylates, ormixtures thereof, such as n-butyl acrylate, iso-butyl acrylate,tert-butyl acrylate, and 2-butyl acrylate, and the corresponding butylmethacrylates: n-butyl methacrylate, iso-butyl methacrylate, tert-butylmethacrylate, and 2-butyl methacrylate, and furthermore methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, propylacrylate, or propyl methacrylate. The monomers may also be used in anycombination. The monomers of group (b) and the group (iv), respectively,may each be a mixture of at least two isomeric butyl acrylates. Themonomer component (b) may be tert-butyl acrylate and/or tert-butylmethacrylate. The monomer component of the group (iv) may be tert-butylacrylate and/or tert-butyl methacrylate.

Suitable monomers of the group (c) and the group (v) may be selectedfrom further ethylenically unsaturated monomers, such as ethylhexylacrylate, stearyl acrylate, stearyl methacrylate, and further esters ofacrylic and methacrylic acid with alcohols which have more than four Catoms, and furthermore acrylonitrile, methacrylonitrile, acrylamide,vinyl acetate or anionic comonomers, such as acrylic acid, methacrylicacid, styrenesulphonic acid.

Particularly preferred monomers of group (d) may be selected fromacrylic acid, and/or styrenesulphonic acid.

The monomers of the first polymer blend are chosen in the secondpolymerization stage so that the glass transition temperature of theresulting copolymer is from −15 to +80° C. Preferably the glasstransition temperature of the copolymer in the second polymerizationstage is from 25 to 75° C.

The first ethylenically unsaturated monomer blend may comprise up to 75%by weight of monomer(s) of group (a) of the total weight of the firstethylenically unsaturated monomer blend. However, the presence monomersof group (a) is not required. Thus the amount of monomer(s) of group (a)may be 0%. Preferably the amount of monomer(s) of group (a) is 0 to 50%by weight, more preferably 5 to 45% by weight, of the total weight ofthe first ethylenically unsaturated monomer blend.

The first ethylenically unsaturated monomer blend may comprise up to100% by weight of monomer(s) of group (b) of the total weight of thefirst ethylenically unsaturated monomer blend.

The prevailing monomer(s) of the first ethylenically unsaturated monomerblend may be either monomer(s) of group (a) or monomer(s) of group (b).Preferably the amount of monomer(s) of group (b) is over 50%, morepreferably from 50 to 100% by weight, even more preferably 55 to 95% byweight, of the total weight of the first ethylenically unsaturatedmonomer blend.

The first ethylenically unsaturated monomer blend may also comprise upto 10% by weight of monomer(s) of group (c) of the total weight of thefirst ethylenically unsaturated monomer blend. However the presencemonomer(s) of group (c) is not required. Thus preferably the amount ofmonomer(s) of group (c) is 0%.

The second polymerization stage is carried out as a rule by a procedurewherein the monomers of the first monomer blend, either individually oras a mixture, and the free radical initiators suitable for initiatingthe polymerization are added to the aqueous prepolymer composition (B).

The second polymerization stage can be carried out either by a feedprocess and by a batch process at temperatures from 40 to 105° C.,preferably from 50 to 100° C. If the polymerization temperature shouldbe above the boiling point of the solvent used, the polymerization iscarried out under superatmospheric pressure, for example in an autoclaveequipped with a stirrer.

Both polymerization stages are usually carried out in the absence ofoxygen, preferably in an inert gas atmosphere, for example undernitrogen. During the polymerization, thorough mixing with the aid of asuitable stirrer should be ensured.

In the second polymerization stage a water-soluble redox system isutilized for initiating the polymerization. The oxidant of the redoxsystem can be for example, hydrogen peroxide, sodium peroxo-disulfate,potassium peroxodisulfate, ammonium peroxodisulfate. The reductant canbe for example reducing agent such as sodium sulfite, sodiumpyrosulfite, sodium bisulfite, sodium dithionite, sodiumhydroxymethanesulfinate or ascorbic acid, or metal salt such as cerium,manganese or iron(II) salt. Preferably hydrogen peroxide is utilized asthe first free-radical initiator. Suitable water-soluble initiatorsystems include redox systems comprising as a redox system hydrogenperoxide and metal ions such as cerium, manganese or iron(II) salts. Aredox system comprising hydrogen peroxide and an iron(II) salt, such asiron(II)sulfate, gives fine-particled dispersions.

In the second polymerization stage polymerization is usually carried outin such a way that the metal salt of the redox system, such as, forexample, the iron(II) salt, is added to the batch before thepolymerization, while hydrogen peroxide is added in simultaneously withthe monomers but separately. Iron(II) salt is usually used inconcentrations of 5 to 200 mg/L Fe⁺⁺ ion, based on the total dispersion,higher or lower concentrations also being possible. Hydrogen peroxide(calculated as 100%) is added in concentrations of 0.2 to 2.0% byweight, based on monomer.

Polymerization with the redox system comprising hydrogen peroxide andmetal ions gives fine-particled dispersions having a good sizing effect.

Completion of the polymerization may be ensured for example by additionof an oil-soluble, sparingly water-soluble free radical initiator. Theoil-soluble, sparingly water-soluble free radical initiators arepreferably added continuously during the addition of the second monomerbatch for subsequent activation after the polymerization with thewater-soluble redox system, and the polymerization is completedtherewith.

Suitable oil-soluble, sparingly water-soluble free radical initiatorsare, for example, customary organic peroxides, such as dibenzoylperoxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, cumylhydroperoxide or bis-cyclohexyl peroxydicarbonate. Here, sparinglywater-soluble is intended to mean that less than 1% of the organicperoxide is completely soluble in water at room temperature.

In this case, polymerization is first carried out, for example, withhydrogen peroxide and iron(II)sulfate, based on monomer used, and, forexample, an oil-soluble, sparingly water-soluble organic peroxide isthen added for subsequent activation, it being possible to achieve aconversion >99.8% and a residual monomer content <100 ppm and todispense with monomer removal.

The copolymerization in the second polymerization stage may further beeffected in the presences of a chain transfer agent. Suitable chaintransfer agents are, for example, sulfur compounds, e.g. mercaptans, diand polysulfides, esters and sulfides of thio- and dithiocarboxylicacids and enol sulfides. Halogen compounds, aldehydes, ketones, formicacid, enol ethers, enamines, hydroxylamine, halogenated hydrocarbons,alcohols, ethylbenzene and xylene may also be used. Examples ofregulators based on sulfur containing organic compounds includemercaptoethanol, mercaptopropanol, mercaptobutanol, thioglycolic acid,thioacetic acid, thiopropionic acid, 1-dodecanthiol, thioethanolamine,sodium dimethyidithiocarbamate, cysteine, ethyl thioglycolate,trimethylolpropane trithioglycolate, pentaerythrityl tetra(mercaptopropionate), pentaerythrityl tetrathioglycolate,trimethylolpropane tri(mercaptoacetate), butylmethylenebisthioglycolate, thioglycerol, glyceryl monothioglycolate,n-octadecyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan,butyl mercaptan, thiophenol, mercaptotrimethoxysilane andacetylcysteine. Preferably the chain transfer agent is dodecylmercaptane.

The concentration of polymer in the obtained aqueous polymer dispersion(A) is typically between 10 and 50% by weight, preferably between 20 and40% by weight.

The obtained aqueous polymer dispersion (A) has a very small particlesize of D50 of less than 90 nm, preferably from 80 to 10 nm, morepreferably from 60 to 10 nm, most preferably from 40 to 10 nm. D90 isless than 150 nm, preferably from 130 to 10 nm, more preferably from 110to 10 nm and most preferably from 90 to 10 nm. The particle size can bedetermined, for example, by laser correlation spectroscopy or byturbidity measurement.

The present surface sizing composition comprises a metal salt, whereinthe metal of said metal salt may be selected from the group of metalswhich have at least 3 valence electrons, for example manganese, iron andaluminium, and any combination thereof. The metal salt may for examplebe selected from the group of carbonates, formiates, acetates, nitrates,sulfates, bromides, and chlorides, and any combination thereof. Examplesof metal salts are selected from the group aluminium sulfate, alum,aluminium chloride, aluminium nitrate, polyaluminium sulfate (PAS),polyaluminium chloride (PAC), and polyaluminium chloride sulfate (PACS),polyaluminium formiate, polyaluminum nitrate, and any combinationthereof. Preferred metal salts are polyaluminium sulfate, aluminiumsulfate, and/or polyaluminium chloride.

The surface sizing composition may further comprise alkylketene dimer(AKD) or rosin.

The metal salt may constitute 0.1-70% by weight of dry content of thesurface sizing composition, preferably 0.5-65% by weight of dry contentof the surface sizing composition, more preferably 1-55% by weight ofdry content of the surface sizing composition and most preferably 5-45%by weight of dry content of the surface sizing composition. The drycontent of the surface sizing composition is herein the dry content ofthe metal salt and polymer dispersion.

The surface sizing composition comprising the metal salt and the aqueouspolymer dispersion may have a viscosity ≤500 mPas, preferably in therange of 0.5-500 mPas, preferably 1-100 mPas, more preferably 1-50 mPas,most preferably 1.5-30 mPas after being stored 1 week at 40° C.,preferably 4 weeks at 40° C., and more preferably 12 weeks at 40° C.,measured at 25° C., by using Brookfield LVDV viscometer with spindle 18and using the highest feasible rotation speed for the spindle.

The surface sizing composition comprising the metal salt, the aqueouspolymer dispersion, and the AKD and/or rosin may have viscosity ≤500,preferably in the range of 0.5-500 mPas, preferably 1-100 mPas, morepreferably 1-50 mPas, most preferably 1.5-30 mPas after being stored 1week at 40° C., and preferably 4 weeks at 40° C., measured at 25° C., byusing Brookfield LVDV viscometer with spindle 18 and using the highestfeasible rotation speed for the spindle.

The surface sizing composition comprising the metal salt and the aqueouspolymer dispersion may have a particle size of D50 of less than 100 nm,preferably from 90 to 10 nm, more preferably from 70 to 10 nm and mostpreferably from 50 to 11 nm after being stored 1 week at 40° C.,preferably 4 weeks at 40° C., and more preferably 12 weeks at 40° C.

The surface sizing composition comprising the metal salt, the aqueouspolymer dispersion, and the AKD and/or rosin may have a particle size ofD50 of less than 200 nm, preferably from 190 to 10 nm, more preferablyfrom 140 to 10 nm and most preferably from 90 to 10 nm after beingstored 1 weeks at 40° C., and preferably 4 weeks at 40° C.

The surface sizing composition may further comprise natural or modifiedpolysaccharides, or derivatives thereof. The polysaccharides may beselected from the group of starches. The starch may be modified, forexample, degraded, oxidized, cationized, dextrin, or otherwisederivatized starch or treated with a combination of the different starchtreatments.

Provided herein is a surface sizing composition comprising an aqueouspolymer dispersion and a metal salt as defined herein. The surfacesizing composition is typically provided in an aqueous liquid vehicle,as an aqueous solution or dispersion, although small amounts ofwater-soluble or water miscible organic solvent(s) may also be present.The surface sizing composition solution typically includes, along withthe sizing compounds, starch. Typically the aqueous dispersion isapplied on the surface in a starch solution. The starch may be modified,for example, degraded, oxidized, cationized, dextrin, or otherwisederivatized starch or treated with a combination of the different starchtreatments. The starch concentration is preferably from 1% to 30%, morepreferably from 5 to 25% and the sizing agent, concentration is from 0.1to 20% by weight, preferably 0.5 to 5.0% by weight, based on the weightof dry starch.

The surface sizing composition disclosed herein also may be used inconjunction with or serially with other additives conventionally used inthe production of paper and other cellulosic products. Such additionaladditives commonly known in the art include, but are not limited to,dispersing agents, antifoaming agents, colorants, inorganic pigments andfillers, anti-curl agents, additional conventional components such assurfactants, plasticizers, humectants, defoamers, UV absorbers, lightfastness enhancers, polymeric dispersants, dye mordants, opticalbrighteners, leveling agents, rheology modifiers, and strengthadditives, to enhance the sizing performance, and improve runnability ofa size press, and otherwise adjust the surface properties.

The present surface sizing compositions are suitable for surface sizingof cellulosic products, in particular all paper and paper boardqualities produced in practice, which may be unsized or may be presizedin the paper pulp, for example with alkylketene dimer, alkenylsuccinicanhydride or rosin.

The specific techniques used to size paper and other cellulosic productssuch as cardboard, include, but are not limited to, those techniquesthat are commonly employed in papermaking to apply the sizingcomposition to the cellulose-based product. The surface sizingcomposition may be provided as a liquid or a foam onto thecellulose-based product. For instance, the aqueous sizing compositionmay be applied to the surface of the paper using a puddle or film sizepress or a size press by using a calender or a doctor knife blade.Alternatively, the sizing composition may be sprayed onto the paper webor be applied by dipping the paper into the aqueous surface sizingcomposition. Paper or other cellulosic product treated with the surfacesizing solution is then dried at elevated temperatures, typicallytemperature of the paper is from 80 to 110° C.

Drying the paper web is typically sufficient to bring the surface sizeand surface strength to full development.

The present invention further provides a method of surface sizing acellulosic product, in particular paper, board or cardboard, comprisingapplying, typically to at least one surface of the cellulosic product, asizing composition comprising an aqueous polymer dispersion and metalsalt as defined herein. Further accordingly provided herein is a papersurface-sized with surface sizing composition as defined herein.

Accordingly further provided herein is a cellulosic productsurface-sized with a surface sizing composition comprising an aqueouspolymer dispersion and a metal salt as defined herein.

The paper, paper board or other cellulosic product onto which thesurface sizing composition comprising the present aqueous polymerdispersions is applied may vary widely and is independent of the kind ofpulp used to make the paper. Surface sizing compositions comprising theaqueous polymer dispersions and metal salt disclosed herein are suitablefor the preparation of sized paper of any thickness and of any kind andthus applicable to papers or cardboards obtained from any specific paperpulp and mixtures thereof.

The present compositions are particularly suitable for surface sizingcellulosic products when the cellulosic product comprises recycledfiber.

The paper or other cellulosic product also may contain additives such asfillers, dyestuffs, paper strengthening agents, drainage rate improvers,and internal sizing agents.

Water absorptiveness of paper surface sized with the present surfacesize composition can be determined using the Cobb 60 method, ISO535:1991(E), at 23° C., 50% relative humidity.

The present composition product may be used in papermaking. The presentinvention provides a method of producing a paper product, comprising thesteps of:

-   -   providing a surface sizing composition according to the present        invention,    -   applying said composition onto a paper product after a headbox        of a papermaking process.

Said composition may be applied at the sheet forming. The compositionmay be applied at or after initiation of sheet forming, such as at asize press.

The present surface sizing composition may be used for surface sizing acellulosic product. The surface sizing composition may be used in apapermaking process. The surface sizing composition may be sprayed ontoa cellulosic product, such as a paper sheet.

The present invention provides a cellulosic product surface sized withsaid surface sizing composition. Said cellulosic product may be selectedfrom paper, board, cardboard, carton, linerboard, and fiberboard.

EXAMPLES

The particle size of the surface sizing compositions was measured usingZetasizer Nano-device. The solids contents were measured using a MettlerToledo Halogen moisture analyzer. The viscosities were measured at 25°C., with Brookfield LVDV viscometer, in a small sample adapter withspindle 18, 60 rpm. The viscosity of the comparative examples 1 and 2was over the measuring range of spindle 18, 60 rpm. They were measuredat 25° C., with Brookfield LVDV viscometer with spindle 31. Thecomparative example 1 with 30 rpm, and the comparative example 2 with0.3 rpm. The viscosity result OMR was over measurement range of spindle31, 0.3 rpm or, because of the high viscosity, the sample could not beinserted uniformly to the small sample adapter to have a reliableresult. When the particle size D50 result was Not Measurable, the samplecould not be dispersed for the measurement to have a reliable result onthe measuring range of Zetasizer Nano.

Example 1 (Formulate of Quaternary Amine Polymer Dispersion with PAC)

The 40 g of 30% quaternary amine groups containing poly(styrene butylacrylate) dispersion was placed in a glass reactor. To the stirringdispersion was added 50 g of water, and subsequently 10 g of 18poly(aluminium chloride) solution. pH of the solution was adjusted to3.3 with sodium hydroxide solution. The mixture was stirred 20 minutesat room temperature. The solids content of the formulation was 14%.

Example 2 (Formulate of Quaternary Amine Polymer Dispersion withAluminum Sulfate)

The 70 g of 30% quaternary amine groups containing poly(styrene butylacrylate) dispersion was placed in a glass reactor. To the stirringdispersion was added 30 g of 39% aluminium sulfate solution. pH of thesolution was adjusted to 3.3 with sodium hydroxide solution. The mixturewas stirred 20 minutes at room temperature. The solids content of theformulation was 33%.

Example 3 (Formulate of Quaternary Amine Polymer Dispersion withAluminium Sulfate and AKD Dispersion)

The 62.5 g of 30% quaternary amine groups containing poly(styrene butylacrylate) dispersion was placed in a glass reactor. To the stirringdispersion was added 4 g of water, 5 g of 39% aluminium sulfatesolution, and 33.5 g of 17% AKD dispersion. pH of the solution wasadjusted to 3.3 with sodium hydroxide solution. The mixture was stirred20 minutes at room temperature. The solids content of the formulationwas 25%.

Comparative Example 1 (Formulate of Tertiary Amine Polymer Dispersionwith PAC)

The 40 g of 30% tertiary amine groups containing poly(styrene butylacrylate) dispersion was placed in a glass reactor. To the stirringdispersion was added 50 g of water, and subsequently 10 g of 18%poly(aluminium chloride) solution. pH of the solution was adjusted to3.3 with sodium hydroxide solution. The mixture was stirred 20 minutesat room temperature. The solids content of the formulation was 14%.

Comparative Example 2 (Formulate of Tertiary Amine Polymer Dispersionwith Aluminium Sulfate)

The 70 g of 30% tertiary amine groups containing poly(styrene butylacrylate) dispersion was placed in a glass reactor. To the stirringdispersion was added 30 g of 39% aluminium sulfate solution. pH of thesolution was adjusted to 3.3 with sodium hydroxide solution. The mixturewas stirred 20 minutes at room temperature. The solids content of theformulation was 33%.

Comparative Example 3 (Formulate of Tertiary Amine Polymer Dispersionwith Aluminium Sulfate and AKD Dispersion)

The 62.5 g of 30% tertiary amine groups containing poly(styrene butylacrylate) dispersion was placed in a glass reactor. To the stirringdispersion was added 4 g of water, 5 g of 39% aluminium sulfatesolution, and 33.5 g of 17% AKD dispersion. pH of the solution wasadjusted to 3.3 with sodium hydroxide solution. The mixture was stirred20 minutes at room temperature. The solids content of the formulationwas 25%.

TABLE 1 24 hours after 1 week after 4 weeks after 12 weeks after Afterthe the preparation. the preparation. the preparation. the preparation.preparation Stored at 40°C. Stored at 40° C. Stored at 40° C. Stored at40° C. Viscosity D50 Viscosity D50 Viscosity D50 Viscosity D50 ViscosityD50 mPas nm mPas nm mPas nm mPas nm mPas nm Example 1 Formulate of 2 263 34 3 36 3 33 quaternary amine polymer dispersion with PAC Example 2Formulate of 7 27 5 29 5 31 8 33 quaternary amine polymer dispersionwith aluminium sulfate Example 3 Formulate of 5 27 13 36 15 38 25 34quaternary amine polymer dispersion with aluminium sulfate and AKDdispersion Comparative Formulate of tertiary 935 26 OMR 275 OMR not OMRnot OMR not Example 1 amine polymer measur- measur- measur- dispersionwith PAC able able able Comparative Formulate of tertiary 95200 35 OMR194 OMR not OMR not OMR not Example 2 amine polymer measur- measur-measur- dispersion with able able able aluminium sulfate ComparativeFormulate of tertiary 14 41 OMR 249 OMR not OMR not OMR not Example 3amine polymer measur- measur- measur- dispersion with able able ablealuminium sulfate and AKD dispersionCationic Formulations for Sizing Tests

The surface sizes and formulations were tested for the surface sizeapplication using an internally unsized, recycled fiber linerboard withbase weight of ca 110 g/m². A Mathis size press was used for thesetests. The surface size formulation was added to surface size starch(C*film 07312) solution at 10% solids content. Hydrophobic polymers wereadded at concentrations of 2, 4 and 6 weight-%. Sizing tests werecarried out at 60° C. temperature. Temperature of the size press nip wasmeasured with Reatec NO1 temperature indicator strips and temperature ofthe water bath for size press rolls was adjusted to obtain the desiredtemperature. The sheets were run through a horizontal pond size press at2 m/min (2 Bar). The sheets were dried at 95° C. using a drum dryer.Temperature of the dryers was adjusted using Reatec NO82 temperatureindicator strips. The sizing efficiency was determined by measuringCobb60 sizing degree according to standard ISO 535.

FIG. 1 shows water absorptiveness of paper surface sized with thequaternary amine groups containing poly(styrene butyl acrylate)dispersion alone, and in the formulate with PAC according to theexample 1. The sizing results disclosed relates to use of the presentaqueous polymer dispersion (cationic polystyrene acrylate based surfacesizing agent (SAE), with quaternary amine acrylates) and present surfacesizing agent (formulation of SAE and PAC). The PAC dose is not includedin the dose calculation of the polymeric size. In the results, a lowerCobb value means better the sizing performance. The graph shows bettersizing performance for the use of the present surface sizing agentcompared to the quaternary sizing polymer alone up to Cobb level of 35g/m².

FIG. 2 shows the sizing results of using SAEs with quaternary aminegroups containing poly(styrene butyl acrylate) dispersion alone, and theformulate with aluminium sulfate, and alkyl ketene dimer (AKD) accordingto the example 3. It is to be noted that AKD emulsions contain aluminiumsulfates. AKD is included in the dose calculation of the polymeric size.As a low Cobb value means better sizing performance, the FIG. 2 clearlyindicate the combined formulation to showing better sizing performancethan the quaternary sizing polymer alone.

The invention claimed is:
 1. A surface sizing composition comprising: ametal salt, wherein the metal has at least 3 valence electrons, whereinthe metal salt is selected from the group of aluminium sulfate,aluminium chloride, aluminium nitrate, polyaluminium sulfate (PAS),polyaluminium chloride (PAC), and polyaluminium chloride sulfate (PACS),polyaluminium formiate, polyaluminium nitrate, and any combinationthereof; and an aqueous polymer dispersion, wherein the aqueous polymerdispersion is an aqueous polymer dispersion (A) and an aqueousprepolvmer composition (B), wherein the aqueous polymer dispersion (A)is obtainable by free radical emulsion copolymerizing a firstethylenically unsaturated monomer blend comprising (a) 0 to 75% byweight of at least one optionally substituted styrene, (b) 15 to 100% byweight of at least one C1-C4-alkyl (meth)acrylate, and (c) 0 to 10% byweight of other ethylenically unsaturated copolymerizable monomers,wherein the sum (a)+(b)+(c) is 100%, in the presence of a water-solubleredox system comprising a first free radical initiator for the freeradical emulsion copolymerization and wherein the aqueous prepolymercomposition (B) is obtainable by free radical emulsion copolymerizing ina polymerization solvent comprising C1-6-carboxylic acid andC1-6-carboxylic acid anhydride, a second ethylenically unsaturatedmonomer blend comprising (i) 5 to 50% by weight of at least oneethylenically unsaturated quaternary amine selected from quaternary saltof N,N,N-tri(C1-4-alkyl)amino C1-4-alkyl(meth)acrylate with a mineralacid or an organic acid and/or quaternary salt ofN,N,N-tri(C1-4-alkyl)amino C1-4-alkyl(meth)acrylamide with a mineralacid or an organic acid, (ii) 0 to 40%, preferably 0%, by weight of atleast one ethylenically unsaturated tertiary amine selected fromN,N-di(C1-4-alkyl)amino C1-4-alkyl(meth)acrylate and/orN,N-di(C1-4-alkyl)amino C1-4-alkyl(meth)acrylamide, (iii) 10 to 95% byweight of at least one optionally substituted styrene, (iv) 0 to 50% byweight of at least one C1-C4-alkyl (meth)acrylate, and (v) 0 to 10% byweight of other ethylenically unsaturated copolymerizable monomers,wherein the sum (i)+(ii)+(iii)+(iv)+(v) is 100%, in the presence of asecond free radical initiator, and adding water to the obtained polymerdispersion to obtain the aqueous prepolymer composition (B).
 2. Thecomposition according to claim 1, wherein the ethylenically unsaturatedquaternary amine (i) is [2-(methacryloyloxy)ethyl]trimethylammoniumchloride or [2-(acryloyloxy)ethyl]-trimethylammoniumchloride.
 3. Thecomposition according to claim 1, wherein the C1-6-carboxylic acid isacetic acid; and/or the C1-6-carboxylic anhydride is acetic anhydride.4. The composition according to claim 1, wherein monomer component (b)and the monomer component (iv) each is a mixture of at least twoisomeric butyl acrylates.
 5. The composition according to claim 1,wherein monomer component (b) is tert-butyl acrylate and/or tert-butylmethacrylate.
 6. The composition according to claim 1, wherein thewater-soluble redox system is a combination of hydrogen peroxide and atleast one metal ion selected from a group consisting of cerium,manganese, and iron(II).
 7. The composition according to claim 1,wherein the metal of said metal salt is selected from the groupmanganese, iron and aluminium, and any combination thereof; and/or themetal salt constitutes 0.1-70% by weight of dry content of the surfacesizing composition.
 8. The composition according to claim 1, wherein thesizing composition further comprises natural or modified polysaccharidesselected from starch, enzymatically degraded starch, and oxidativelydegraded starch, and derivatives thereof.